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The effect of weather on golf shots
Topic Started: February 18 2012, 02:32 AM (197 Views)
Fergal (IWO)
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Different weather conditions have a bigger effect on golf shots than you might think, and is something that should be considered at different times of the year.

Consider two scenarios - a cold dry frosty morning in winter (say 0 °C, RH 80%, with frost on the ground) and a warm humid afternoon in summer (say 25 °C, RH 70%, strong sunshine). Assume no wind in both cases and we're playing the same course (so same altitude, say near sea level).

Air density and ball temperature are the two factors directly affecting the flight of the ball (neglect the effects on the player and club shaft!).

Air density is dependent on air temperature, specific humidity, pressure and altitude. Assume altitude and pressure are the same in both scenarios, so only temperature and specific humidity are different (by specific humidity I mean the actual amount of water vapour in the air (grams per kilo of air) as opposed to relative humidity, which is the percentage of water vapour in the air compared to the maximum it could hold at that temperature (warmer air can hold more water vapour than colder air). The air density for the two scenarios is

Winter 1.286 kg/m³
Summer 1.170 kg/m³

The aerodynamic drag on a golf ball is directly related to the air density, with lower density producing lower drag. So the percentage difference between the drag on the ball is just the difference in densities (i.e. around 10%). That means a 10 yard difference for every 100 yards of distance, so a wintertime carry of 220 yards could be around 245 yards in summer, all other things equal.

But all other things aren't equal. The temperature of the ball has a big effect. They say the optimum temperature of a golf ball is around 27 °C, as that's where the compression is greatest. It takes around 6 hours for the ball to fully warm to this temperature to its core, so storing it indoors overnight prior to a round can gain you a few yards.

During a round of golf the ball spends most of its time lying on the ground, and is only in the air a tiny fraction of the time. Therefore ground temperature will determine its temperature. In winter, with frost on the ground (assume they didn't close the course!) the ground temperature could be as low as -10 °C and temperature of the ball will fall quickly during the round, and will be at its coldest on the 18th. You could of course keep a ball in your pocket and alternate balls every hole to slow down this cooling process but it will still cool down overall. In summertime, with strong sunshine, the ground could be 30 °C or more, so the ball should hold its temperature right throughout the round. As the core materials are more elastic at this temperature, plus the ground will probably be harder, the bounce and roll will be much bigger than in winter.

So we have the 10% increase due to different air densities plus the effect of a warmer ball and harder ground (not to mention the physical state of the player). We could be looking at 20-30% longer drives and using around 1-2 irons less in summer versus winter. The longest distances will be in warm muggy low pressure systems while the shortest will be in early morning in cold dry high pressure systems.

Of course in reality we get a much smaller spread in contitions throughout the year, with most rounds probably played between 10-20 °C, but it might be interesting to compare your distances now to those in a few months' time (assuming wind conditions are the same).
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ConorLK
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Fascinating stuff as always Fergal!

We always take air density of 1.2kg/m^3 as a standard in my line of study, (quite ignorantly) I wasn't aware it fluctuated by such a relatively large degree depending on conditions, it could actually have quite a noticeable difference if the actual density was calculated

I haven't played a single round of golf since last Summer but generally I'm quite a keen player, obviously the effect of the wind will negate any temperature effect most of the time but I'd love to see the scenario you mention played out to see if it made a real difference, 25 yards can be a huge difference for identical swings with the same wind conditions
Edited by ConorLK, February 18 2012, 03:53 AM.
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Fergal (IWO)
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Well 1.2 is a fairly good approximation for low-level locations.

Here's a density calculator

http://www.denysschen.com/catalogue/density.aspx

Density is also related to atmospheric pressure, so will be lower on days where pressure is lower, and vice versa. When putting in your elevation in the calculator above, which is based on the standard atmosphere, you should really put in the day's pressure altitude, i.e. the altitude in a standard atmosphere that corresponds to the actual pressure right at your location and altitude on the day. In days where surface pressure is less than the standard 1013.25 hPa, PA will be higher because your pressure would be found at a higher altitude in a standard atmosphere. Pressure falls by 1 hPa every 8 metres or so, so if say surface pressure is 990 hPa (23 hPa less than standard) then the pressure altitude of sea level will be 23x8 = 184 metres, i.e. an aeroplane at sea level with standard pressure setting in its altimeter would think it was at 184 metres (600 ft).

You can calculate pressure altitude here (Select Density/Press Altitude)
http://ows.public.sembach.af.mil/index.cfm?section=Tools
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